This invention relates to an improved, viscous-fluid, rotary timer. The rotary timer of this invention was developed for use in lightweight model aircraft. In the sport of hand-launched glider flying, model gliders are designed to stay aloft indefinitely where suitable currents provide the necessary lift. Because the flyer desires to terminate the flight at some reasonable time after initiation, means must be provided to return the aircraft to the ground for recovery. The timer is utilized to initiate a mechanical actuation, for example changing the attitude of the horizontal stabilizer thereby stalling the plane to the ground. Given a one or two ounce total glider weight, the combined weight of timer and actuator must be such that it does not significantly affect the quality of the glider's flight.
It has been found that a viscous-fluid rotary timer is well suited for such an application. Heretofore, as described in the patent of Hadfield U.S. Pat. No. 3,712,421, issued Jan. 23, 1973, entitled "Rotary Timer", a comparable timer has been suggested for use in missile or projectile fusing applications where its freedom from gravitational effects was considered advantageous. However, when the Hadfield device is run through the range of rotational speeds it will sustain in human hands, the viscous fluid medium is pumped past one or both journal seals thereby comprising its accuracy.
Improvements were made to the viscous-fluid rotary timer of the type described by Hadfield to:
a. Improve it's accuracy; PA1 b. Extend it's ability to handle varying rotational inputs; PA1 c. Better it's efficiency. This is to increase the amount of uniform retarding force generated by the rotor while decreasing the rotor mass.